A 3-cell Flow-Mix Calorimeter was designed and built. In comparison with the existing one-cell calorimeter, this new one is completely solid-state thermostated (uses no external waterbath). This instrument operates at four temperatures regimes. Using three cells heat obtained from the reaction between the reagents and buffer (heat of dilution) is electronically subtracted during the mixing from the one coming from the reaction cell where both reactants are mixed. As a result, the output signal corresponds to the heat of binding between the two reactants. This mode of operation minimizes the propagation of errors and increases the overall accuracy in the performed measurements.